Exemplary embodiments of the invention relate to a drive device for a motor vehicle, in particular an electric vehicle or a motor vehicle comprising at least one drive axle that is driven purely electrically.
A drive device for an electric vehicle is already known from WO 2012/010340 A1, comprising an electric motor, an axle drive, and a multistep reduction gear arranged between the electric motor and the axle drive.
DE 25 21 831 A1 discloses a drive device that comprises a multistep reduction gear having three planetary gear stages, a transmission input element being permanently connected to a sun gear of the first planetary gear stage for conjoint rotation, a transmission output element being permanently connected to the planet carrier of the third planetary gear stage for conjoint rotation, and the planet carrier of the first planetary gear stage and the sun gear of the third planetary gear stage being permanently interconnected for conjoint rotation.
The invention, in particular, is directed to providing a developed drive device for an electric vehicle.
According to the invention, a drive device is proposed, in particular for an electric vehicle, comprising at least one electric motor, at least one axle drive and at least one multistep reduction gear that is arranged between the electric motor and the axle drive, which is intended at least in structural terms for shifting two forward gears and comprises precisely three planetary gear stages that are operatively interconnected and comprise sun gears, internal gears and planet carriers, at least two shift units, a transmission input element for attaching the electric motor for conjoint rotation, and a transmission output element for attaching the axle drive for conjoint rotation, the transmission input element being permanently connected to the sun gear of the first planetary gear stage for conjoint rotation, the transmission output element being permanently connected at least to the planet carrier of the third planetary gear stage for conjoint rotation, and at least the planet carrier of the first planetary gear stage and the sun gear of the third planetary gear stage being permanently interconnected for conjoint rotation.
Such a design makes it possible to provide a compact drive device for an electric vehicle that allows for advantageous attachment of the electric motor to the axle drive. The multistep reduction gear can provide various forward gears by means of which a drive torque output by the electric motor can advantageously be converted. Shiftability of reverse gears can be dispensed with by way of the electric motor being designed for a reversal in the direction of rotation. Component stresses can be reduced at least in part in the proposed multistep reduction gear on account of the basic structure thereof, as a result of which, in particular, light-weight construction can be simplified. The differently geared forward gears mean that the electric motor can be operated highly efficiently even at high vehicle speeds. At low speeds, a torque of the electric motor can be advantageously converted. Transmission ratios of the forward gears and/or of the axle drive can be adjusted to an embodiment of the electric vehicle at least in part. A flexible drive device can be provided.
In this context, “drive device comprising at least one electric motor, at least one axle drive and a multistep reduction gear arranged between the electric motor and the axle drive” is intended to mean, in particular, a drive device that only comprises electric motors for generating a drive torque. This is intended to mean, in particular, a drive device that is independent of an internal combustion engine. In this context, a “multistep reduction gear” is intended to mean, in particular, a transmission arranged between the electric motor and the axle drive for shifting the differently geared forward gears. A “planetary gear stage” is furthermore intended to mean, in particular, a gear stage that is defined by intermeshing between a sun gear and a planetary gear guided by a planet carrier, and/or intermeshing between a planetary gear guided by a planet carrier, and an internal gear. In principle, the planetary gear stages can be integral, at least in part. In particular, it is conceivable for two of the planetary gear stages to comprise a common internal gear and separate sun gears, or a common sun gear and separate internal gears. An “axle drive” is intended to mean, in particular, an operative connection between the transmission output element of the multistep reduction gear and at least one driving wheel of the motor vehicle. The axle drive may be intended for permanently connecting the transmission output element and the driving wheel for conjoint rotation. Alternatively, the axle drive may also comprise a differential gear that is intended for attaching two driving wheels to the transmission output element so as to be in parallel.
The planetary gear stages are denoted in the following as “first planetary gear stage”, “second planetary gear stage” and “third planetary gear stage”. The designations “first”, “second” and “third” planetary gear stage are, in particular, intended for specifying an axial arrangement, it being possible for an axial sequence of the planetary gear stages to deviate from the numbering. In principle, a modified arrangement of the planetary gear stages and/or a stacked arrangement in which the planetary gear stages are nested inside one another radially, at least in part, is conceivable. Different, kinematically equivalent transmission structures can be achieved, in particular, by spatially rearranging the shift units, by a different arrangement of transmission elements and/or by swapping the sun gears, planetary gears and/or internal gears. In this case, “kinematically equivalent transmission structures” is intended to mean transmission structures that have the same number of shift units and identical shifting models for shifting the forward gears and the reverse gears.
A “shift unit” is furthermore intended to mean, in particular, a unit comprising exactly two coupling elements that are rotatable relative to one another and are intended to be interconnected for conjoint rotation. A shift unit can optionally be formed as a clutch or as a brake. A shift unit formed as a “clutch” is intended to mean, in particular, a shift unit arranged in a power flow between two of the planetary gear stages and intended to interconnect for conjoint rotation, in a closed state, the two rotatable coupling elements thereof that are rotatable independently of one another in an open state. A shift unit formed as a “brake” is intended to mean, in particular, a shift unit arranged in an operative manner between one of the planetary gear stages and a transmission housing and that is intended, in a closed state, to connect for conjoint rotation the rotatable coupling element thereof that is rotatable independently of the transmission housing in an open state, and the coupling element thereof that is connected to the transmission housing for conjoint rotation. “Connected for conjoint rotation” is intended, in particular, to mean a connection in which a power flow is transmitted so as to have an unchanged torque, an unchanged direction of rotation and/or an unchanged speed, averaged over a complete rotation.
In this context, a shift unit is intended, in particular, not to mean a clutch that is connected upstream or downstream of a gear set formed by the planetary gear stages. A “clutch connected upstream of the gear set” is intended, in particular, to mean a clutch arranged in a power flow between the electric motor and the transmission input element in at least one gear, such as a separating clutch or a starting clutch. A “clutch connected downstream of the gear set” is intended, in particular, to mean a clutch arranged in a power flow between the transmission output element and the axle drive in at least one gear, such as a four-wheel clutch. In principle, shiftability of the multistep reduction gear can be increased by means of a clutch unit upstream or downstream of the gear set. In this case, a “transmission input element” is intended, in particular, to mean a transmission element intended, at least in terms of structure, for attaching a rotor of the electric motor for conjoint rotation. A “transmission output element” is intended, in particular, to mean a transmission element intended, at least in terms of structure, for attaching an axle drive for conjoint rotation. A “transmission element” is intended, in particular, to mean a design intended for permanently connecting the sun gears, planet carriers, internal gears and/or coupling elements for conjoint rotation.
“At least in terms of structure” is intended, in particular, to mean that a corresponding design is provided structurally, but it is possible to refrain from functional use of the structural design in a possible embodiment. In this context, “intended in terms of structure for shifting a gear” is intended, in particular, to mean that the shift units and planetary gear stages can, in principle, mechanically form a corresponding gear, irrespective of whether or not shifting of the gear is omitted within the context of a shifting strategy. For example, in one embodiment, the shift units may be intended in terms of structure for shifting more forward gears than it may be expedient to shift within the context of an operating strategy for the multistep reduction gear.
“Decoupling a planetary gear stage” is intended, in particular, to mean that the planetary gear stage is removed from transmission of a power flow between the transmission input element and the transmission output element. A “shift unit for decoupling a planetary gear stage” is intended to mean an individual shift unit intended merely for attaching the sun gear, the planet carrier or the internal gear of the planetary gear stage to the remaining planetary gear stages. If the shift unit is open, the sun gear, the planet carrier or the internal gear are freely rotatable relative to the sun gears, the planet carriers and the internal gears of the remaining planetary gear stages and to the transmission housing, as a result of which the decoupled planetary gear stage does not have any support for transmitting a torque.
Some of the shift units are preferably designed in an interlocking manner. A drag loss can thus be kept small, with the result that a power loss inside the multistep reduction gear can advantageously be reduced. In this case, a “shift unit designed in an interlocking manner” is intended, in particular, to mean a shift unit comprising toothing and/or claws for connecting the coupling elements thereof or for attaching the coupling elements thereof, which toothing and/or claws mutually engage in an interlocking manner to establish a connection for conjoint rotation, transmission of a power flow in an fully closed state occurring at least mainly by means of an interlocking connection. The shift units can in principle be designed in a frictional or interlocking manner. In this case, a “shift unit designed in a frictional manner” is intended, in particular, to mean a shift unit comprising at least two friction partners for connecting the coupling elements thereof or for attaching the coupling elements thereof, which friction partners are in frictional contact with one another in order to establish a connection for conjoint rotation, transmission of a power flow in a fully closed state occurring at least mainly by means of friction. A clutch unit designed in a frictional manner is preferably designed as a disc clutch unit, and a brake unit designed in a frictional manner is preferably designed as a disc brake unit. A clutch unit designed in an interlocking manner is preferably designed as a claw clutch unit, and a brake unit designed in an interlocking manner is preferably designed as a claw brake unit. A shift unit designed in an interlocking manner is advantageously shiftable by means of a sliding sleeve. In this case, the shift units designed in an interlocking manner are preferably designed without a frictional synchronizer, but may in principle also comprise a frictional synchronizer.
The multistep reduction gear preferably comprises actuators for automated shifting of the shift units. It is in principle also possible, however, to design at least some of the shift units so as to shift automatically at least in part. An automatically shifting clutch unit or brake unit is preferably designed as a freewheeling mechanism. Moreover, a design of the planetary gear stages having single planetary gear sets or double planetary gear sets may also deviate from the embodiments shown. In a kinematically equivalent manner it is possible, for example, to replace a single planetary gear set with a double planetary gear set, it additionally being necessary to, in particular, adjust a stationary transmission ratio of the planetary gear stage in order to achieve kinematically identical operation. In particular in the case of an embodiment using a double planetary gear set, it is in principle also possible to switch an attachment of a sun gear and a planet carrier, an internal gear and a planet carrier, or a sun gear and an internal gear, it additionally being necessary to, in particular, adjust a stationary transmission ratio of the planetary gear stage in order to achieve kinematically identical operation.
In the following, the terms “axial” and “radial” relate, in particular, to the main axis of rotation of the multistep reduction gear, and therefore the expression “axial”, in particular, denotes a direction extending in parallel with or coaxially to the main axis of rotation. Furthermore, the expression “radial”, in particular, denotes a direction extending perpendicularly to the main axis of rotation. “Arranged on the transmission input side” is intended, in particular, to mean that the component in question is arranged on a side of the further component facing the transmission input element and/or the electric motor. “Arranged on the transmission output side” is intended, in particular, to mean that the component in question is arranged on a side of the further component that faces away from the transmission input element and/or the electric motor, even if the further component is arranged after the transmission output element in the axial direction, for example because the transmission output element is arranged between two planetary gear stages.
Further advantages can be seen from the following description of the figures. A plurality of embodiments of the invention are shown in the figures. In order to distinguish the embodiments, the reference signs of the following description of the figures have been supplemented by the letters a to c. With reference to identically denoted components, in particular with reference to components having the same reference signs, reference is in principle made to the description and/or the drawings of the first embodiment having the letter a. The descriptions of the further embodiments are substantially limited to the differences between the embodiments. The figures, the description of the figures and the claims contain numerous features in combination. Expediently, a person skilled in the art will also consider the features individually and combine them to form meaningful further combinations.